In systems employing pulsed laser radiation, it is often desirable to employ a higher repetition rate for the pulsed laser radiation than is commonly available from a single component laser. Techniques, frequently employing rotating optics, are known which permit the sequential combination of pulsed laser radiation beams into a single, common axial beam. These and related techniques are represented by U.S. Pat. Nos. 3,543,183; 3,310,753; 3,541,468; 3,568,087; and 3,924,937.
In one application of high pulse rate laser radiation, isotope separation is accomplished by isotopically selective laser photoionization in a high flow rate environment of plural isotope types. The high flow rate necessitates a high pulse rate if the entire environment is to be illuminated as desired for efficiency. Such high rates normally are obtainable only by combining beams from several lasers. An example of such a use is described in U.S. Pat. No. 3,924,937.
For such an application of laser isotope separation, it is typical to find laser beam paths which extend over substantial distances and therefore require a precise and nonvarying angular orientation and superposition of several different laser beams. For example, it is often desirable to employ one laser oscillator having a precisely determined frequency, called the local oscillator, to control the frequencies of several injection-locked laser oscillators which are often high power devices which cannot operate at the high repetition rate of the local oscillator. Laser pulse durations are typically in the range of a substantial fraction of a microsecond for this use. Where rotating optics are employed to receive each sequential pulse from several lasers in order to combine them at a unitary path, the angular motion of these optics frequently results in motion of the combined laser beams over the pulse duration. This motion may appear as a beam deflection as well as a rotation of the plane of deflection from pulse to pulse. In applications of laser isotope separation which require the consistent illumination of a predetermined channel throughout the environment of isotopes to be separated, such angular motion of the radiation is to be avoided.